Aqueous polyamide resin dispersion and process for producing the same

ABSTRACT

The aqueous dispersion of polyamide resin of the present invention comprises dispersed polyamide resin particles, basic material and water. The dispersed polyamide resin particles have a weight-average diameter of 0.1-10 μm. The ratio of end carboxyl groups to end amino groups in the polyamide resin is between 60/40 and 100/0. The amount of said basic material added is 0.2-3.0 mol per mol of end carboxyl groups. Such an aqueous dispersion of polyamide resin can be manufactured by adding the polyamide resin to an aqueous dispersion medium containing 0.2-3.0 mol of basic material per mol of end carboxyl groups in the polyamide resin.

TECHNICAL FIELD

The present invention relates to an aqueous dispersion of polyamideresin wherein polyamide resin particles are dispersed in an aqueousdispersion medium, and to a method of manufacture thereof.

BACKGROUND ART

Aqueous dispersions of polyamide resin can convey oil a resistance,solvent resistance, chemical resistance, abrasion resistance and gasblocking and adhesive properties and the like when used as a basis inthe formation of coating films. Consequently, aqueous dispersions ofpolyamide resin are widely used in water-color inks, textile treatments,textile fillers, paper treatments, binders, lubricants, steel platefinishing agents, surface modifiers, hot melt adhesives and the like.

It is difficult to prepare a dispersion of polyamide in an aqueousdispersion medium by a direct process of emulsion polymerization in theaqueous dispersion medium because of its manufacturing process.Therefore, various methods have been proposed for manufacturing aqueousdispersions of polyamide resin by dispersion in an aqueous medium ofpolyamide resin formed by condensation polymerization or ring-openingpolymerization. Possible methods of dispersing polyamide resin in anaqueous medium include reprecipitation and post-emulsification.

Reprecipitation is a method of dissolving polyamide resin in an organicsolvent, reprecipitating the polyamide resin and replacing the organicsolvent with an aqueous medium (see for example Japanese PatentApplications Laid-open No. S61-223059 and S63-186738).

The main problems with reprecipitation are the following. First, thepolyamide resin particles obtained from reprecipitation are large indiameter, limiting the uses of the manufactured aqueous dispersion ofpolyamide resin. Second, polyamide resin particles often re-aggregatewhen the organic solvent is replaced with an aqueous medium, so theaqueous dispersion of polyamide resin obtained by reprecipitation islacking in standing stability. Third, the inclusion of the step ofreplacing the organic solvent with an aqueous medium complicates themanufacturing process in the reprecipitation method.

In the post-emulsification method polyamide resin is dispersed in anaqueous medium as follows. In the first step, polyamide resin isdissolved in a non-water-soluble or slightly water-soluble organicsolvent to prepare a polyamide resin solution. In the second step, thepolyamide resin solution is mixed together with an emulsifier in anaqueous medium to prepare a mixture. In the third step, the mixture isagitation emulsified at high shear force in a specialized emulsifyingapparatus. In the fourth step, the organic solvent is removed from themixture, resulting in an aqueous dispersion of polyamide resin.

The main problems with post-emulsification are the following. First,because polyamide resin is not very soluble with respect to organicsolvents, the post-emulsion method has low productivity and cannot becalled economical. Second, because bubbling occurs during removal of theorganic solvent in the post-emulsification method, a process is requiredto control bubbling, complicating the operation and making the methodless economical. Third, the aqueous dispersion of polyamide resinobtained by post-emulsification inevitably contains residues of organicsolvent and emulsifiers. Fourth, the post-emulsification method useslarge quantities of organic solvent which could contaminate the workenvironment and cause environmental a pollution.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to resolve the various issuesdiscussed above.

The aqueous dispersion of polyamide resin provided by the first aspectof the present invention contains dispersed polyamide resin particles,basic material and water, with the dispersed polyamide resin particleshaving a weight-average diameter of 0.1-10 μm and a ratio of endcarboxyl groups to end amino groups being between 60/40 and 100/0, andwith the amount of said basic material being 0.2-3.0 mol per mol of saidend carboxyl groups.

Polyamide resin has carboxyl and/or amino groups on the ends. Ingeneral, carboxyl groups have a relatively low degree of electrolyticdissociation with respect to water. However, coexisting carboxyl groupswith basic material promotes electrolytic dissociation of carboxylgroups in water solution (aqueous dispersion). Consequently, addition ofbasic material to the aforementioned aqueous dispersion of polyamideresin promotes electrolytic dissociation of end carboxyl groups on thedispersed polyamide resin particles, and improves dispersive power withrespect to an aqueous dispersion medium.

The cause of aggregation of dispersed polyamide resin particles isattractive force acting on the particles. One such attractive force canbe attributed to hydrogen bond. The aforementioned dispersed polyamideresin particles have relatively few amino groups in proportion tocarboxyl groups. Consequently, with the aforementioned aqueousdispersion of polyamide resin there is relatively little hydrogenbonding force acting among the dispersed polyamide resin particles, andexcessive aggregation of the dispersed polyamide resin particles istherefore prevented.

Thus, because excessive aggregation of the dispersed polyamide resinparticles is controlled with the aforementioned aqueous dispersion ofpolyamide resin, standing stability is excellent.

An alkali metal hydroxide or amino compound is preferred as the basicmaterial.

Examples of possible alkali metal hydroxide include sodium hydroxide andpotassium hydroxide.

In the present invention, the term “amino compound” also includesammonia.

The method of manufacturing an aqueous dispersion of polyamide resinprovided by the second aspect of the present invention is characterizedby the addition of polyamide resin to an aqueous dispersion mediumcontaining 0.2-3.0 mol of basic material per mol of end carboxyl groupson the polyamide resin.

As mentioned already, electrolytic dissociation of carboxyl groups ispromoted by the coexistence of basic material with polyamide resin,allowing for the prevention of excessive aggregation between polyamideresin particles. The aforementioned method of manufacturing an aqueousdispersion of polyamide resin employs an aqueous dispersion mediumcontaining basic material, providing an aqueous dispersion of polyamideresin with small-diameter polyamide resin particles and excellentstanding stability.

The amount of said basic material in the aforementioned aqueousdispersion medium should be in the range of 0.2-3.0 mol per mol of saidend carboxyl groups. If the amount of said basic material falls belowthis range, aggregation of polyamide resin particles will not besufficiently controlled, making it difficult to obtain an aqueousdispersion of polyamide resin. If the amount of said basic materialexceeds this range, the resulting aqueous dispersion of polyamide resinwill be impractical due to high alkalinity.

Preferably, the amount of said basic material should be 0.4-2.0 mol permol of said end carboxyl groups. Particularly favorable results areobtained if the amount of said basic material is 0.6-1.5 mol.

The ratio of said end carboxyl groups to said end amino groups in thepolyamide resin should be between 60/40 and 100/0.

As mentioned above, amino groups are one cause of aggregation ofpolyamide resin particles because of their susceptibility to hydrogenbonding. The polyamide resin used in the aforementioned method ofmanufacturing an aqueous dispersion of polyamide resin has a relativelysmall number of end amino groups in proportion to end carboxyl groups.Consequently, the aforementioned manufacturing method avoids excessiveaggregation caused by end amino groups, and provides an aqueousdispersion of polyamide resin with excellent standing stability.

The polyamide resin used in the aforementioned method of manufacturingan aqueous dispersion of polyamide resin should have 50-3000 mmol of endcarboxyl groups per kg of said polyamide resin. If the amount of endcarboxyl groups falls below this range, it will be impossible toadequately disperse the polyamide resin in the aqueous dispersionmedium. The upper limit is set at 3000 mmol because there are limits onthe amount of end carboxyl groups that can be introduced into polyamideresin. However, because the dispersive force of polyamide resin inaqueous dispersion medium increases as the amount of end carboxyl groupsin the polyamide resin increases, the amount of end carboxyl groupsshould be as large as is economically feasible.

In order to obtain even better results, the amount of end carboxylgroups in the polyamide resin is in the range of 100-2000 mmol per kg ofpolyamide resin.

In the method of manufacturing an aqueous dispersion of polyamide resinof the present invention, a polyamide resin containing as a structuralunit at least one from the group of —[NH(CH₂)₅CO]—,—[NH(CH₂)₆NHCO(CH₂)₄CO]—, —[(NH(CH₂)₆NHCO(CH₂)₈CO]—, —[NH(CH₂)₁₀CO)]—and —[NH(CH₂)₁₁CO] is used by preference.

Specific examples of polyamide resin include 6-nylon, 66-nylon,610-nylon, 11-nylon, 12-nylon, 6/66 copolymer nylon, 6/610 copolymernylon, 6/11 copolymer nylon, 6/12 copolymer nylon, 6/66/11 copolymernylon, 6/66/12 copolymer nylon, 6/66/11/12 copolymer nylon and6/66/610/11/12 copolymer nylon. In the said method of manufacturing anaqueous dispersion of polyamide resin, the listed polymers or copolymerscan be used individually or more than one can be used in combination asthe polyamide resin.

The polyamide resin used in the said method of manufacturing an aqueousdispersion of polyamide resin can be manufactured by a well-knownmethod. For example, methods that can be used for manufacturing thepolyamide resin include condensation polymerization of diamines withdicarboxylic acids, condensation polymerization of Ω-amino-Ω′-carboxylicacids, or ring-opening polymerization of ring lactams.

Specific examples of diamines include ethylene diamine, trimethylenediamine, tetramethylene diamine, pentamethylene diamine, hexamethylenediamene, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane,1,10-diaminodecane, phenylene diamine, and methaxylilene diamine.

Specific examples of dicarboxylic acids include glutaric acid, adipicacid, pimelic acid, suberic acid, azelaicacid, sebacicacid, nonanedicarboxylic acid, decane dicarboxylic acid, tetradecane dicarboxylicacid, octadecane dicarboxylic acid, fumaric acid, phthalic acid, andxylilene dicarboxylic acid.

Specific examples of Ω-amino-Ω′-carboxylic acids include 6-aminocaproicacid, 7-aminoheptanoic acid, 9-aminononanoic acid, 11-aminoundecanoicacid, and 12-aminododecanoic acid.

Specific examples of ring lactams include ε-caprolactam, Ω-enantholactamand Ω-lauryllactam.

In order to adjust the proportion of end carboxyl groups to end aminogroups in the polyamide resin to between 60/40 and 100/0, a specificamount of a dicarboxylic or monocarboxylic acid can be added as apolymerization regulator during condensation polymerization orring-opening polymerization.

Specific examples of dicarboxylic acids that can be used as the saidpolymerization regulator include glutaric acid, adipic acid, pimelicacid, suberic acid, azelaic acid, sebacic acid, nonane dicarboxylicacid, decane dicarboxylic acid, tetradecane dicarboxylic acid,octadecane dicarboxylic acid, fumaric acid, phthalic acid and xylilenedicarboxylic acid.

Specific examples of monocarboxylic acids that can be used as the saidpolymerization regulator include caproic acid, heptanoic acid, nonanoicacid, undecanoic acid and dodecanoic acid.

Possible basic materials for mixing with the aqueous dispersion mediuminclude alkali metal hydroxides or amino compounds.

Examples of said alkali metal hydroxides include lithium hydroxide,sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesiumhydroxide and francium hydroxide. Of these alkali metal hydroxides,sodium hydroxide and potassium hydroxide are used by preference in thepresent invention since they effectively enhance the dispersive force ofthe polyamide resin.

Well-known amino compounds including ammonia can be used as the saidamino compounds.

The amount of water in the aqueous dispersion medium should be 30-1500parts by weight based on 100 parts by weight of polyamide resin. If theamount of water falls below this range, the polyamide resin cannot beadequately dispersed in the aqueous dispersion medium, while if theamount of water exceeds this range, the concentration of polyamide resinin the resulting aqueous dispersion of polyamide resin will beexcessively low.

In order to obtain still better results, the amount of water is kept inthe range of 100-500 parts by weight based on 100 parts by weight ofpolyamide resin.

A variety of additives including high polymer dispersants, inorganicdispersants, anionic surfactants, nonionic surfactants, ampholyticsurfactants and antioxidants may be added to the aqueous dispersionmedium as long as they do not detract from the properties of theresulting aqueous dispersion of polyamide resin.

Examples of high polymer dispersants include polyacrylate, polystyrenesulfonate, styrene anhydrous maleate, polyvinyl alcohol and hydroxyethylcellulose.

Examples of inorganic dispersants include alumina sol, silica sol andcalcium phosphate.

Examples of anionic surfactants include rosin acid salts, fatty acidsalts and alkylbenzene sulfonate.

Examples of nonionic surfactants include polyoxyethylene alkyl ether,glycerine fatty acid ester and polyoxyethylene fatty acid ethanolamide.

In the preferred embodiments, the polyamide resin is heated to atemperature above the softening point of the polyamide resin fordispersion in the aqueous dispersion medium. Heating the polyamide resinto above this softening point releases the associations betweenmolecules and aggregation among particles. Consequently, the diameter ofthe polyamide resin particles can be minimized. Also, as explainedabove, aggregation (or re-aggregation) among polyamide resin particlesis controlled by the addition of basic material and by the presence ofcarboxyl groups, so the particles of polyamide resin are maintained inthe aqueous dispersion with a small diameter in a suitable dispersedstate.

The heating temperature of the polyamide resin cannot be statedunivocally because it is determined for example according to the meltingpoint of the polyamide resin (the type and degree of polymerization ofthe structural units). However, if the heating temperature is too low,the polyamide does not soften sufficiently and cannot be dispersed inthe aqueous dispersion medium, while if the heating temperature is toohigh the polyamide resin is vulnerable to degradation. Consequently, theheating temperature of the polyamide resin is generally in the range of70-300 or preferably 90-220° C.

Ideally, the polyamide resin is dispersed in the aqueous dispersionmedium by application of shear force to an aqueous dispersion medium towhich the polyamide resin has been added.

When applied to an aqueous dispersion medium to which polyamide resinhas been added, shear force releases associations between moleculesand/or aggregation among particles of the polyamide resin. This resultsnot only in small diameter polyamide resin particles, but also inuniform dispersion of the polyamide resin particles in the aqueousdispersion medium.

Application of shear force to the aqueous dispersion medium can beachieved for example by agitation of the aqueous dispersion medium. Theaqueous dispersion medium can be agitated for example by rotation ofmixing blades. In this case, the rotational frequency of the mixingblades is set for example at 100-500 times a minute. The rotationalfrequency of the mixing blades is set above 100 times a minute in orderto obtain an adequate agitation effect. Rotation of the mixing bladesover 500 times a minute provides no benefit proportional to theincreased rotation and only increases costs.

BEST MODE FOR CARRYING OUT THE INVENTION

The following are two possible means of manufacturing the aqueousdispersion of polyamide resin of the present invention.

The first manufacturing method comprises the following steps.

In the first step, specific quantities of polyamide resin, water andbasic material are supplied in one batch to a dispersion tank.

In the second step, the aqueous dispersion medium is agitated using amixing blade at 100-500 rpm while being heated to a temperature abovethe softening temperature of the polyamide resin in the aqueousdispersion medium, raising the temperature of both aqueous dispersionmedium and polyamide resin.

In the third step, the temperature of both aqueous dispersion medium andpolyamide resin is maintained at a temperature above the softeningtemperature of the polyamide resin, while agitation is continued forabout 10-60 minutes using a mixing blade at 100-500 rpm.

The second manufacturing method comprises the following steps.

In the first step, a dispersion tank is first heated to a temperatureabove the softening temperature of the polyamide resin in the aqueousdispersion medium, and kept under pressure.

In the second step, the heating and pressure conditions of thedispersion tank are maintained, and fixed amounts of melted polyamideresin, water and basic material are added separately one after anotherto the dispersion tank with a mixing blade being rotated at 100-500 rpm.

In the third step, agitation is continued for about 10-60 minutes usinga mixing blade at 100-500 rpm while maintaining the dispersion tank at atemperature above the softening temperature of the polyamide resin inthe aqueous dispersion medium.

The dispersion tank used in the aforementioned methods may be anypressure proof container equipped with a means for heating to atemperature above the softening temperature of the polyamide resin inthe aqueous dispersion medium and a means of agitation sufficient toapply shear force to the contents. For example, a pressure proofautoclave equipped with an agitator can be used as the dispersion tankin the aforementioned manufacturing methods.

In either one of the aforementioned manufacturing methods, the polyamideresin is subject to shear force from agitation while in a softened statein the aqueous dispersion medium. Consequently, the associations betweenmolecules and aggregations of particles of the polyamide resin arereleased, the particle diameter is minimized, and dispersal is uniformin the aqueous dispersion medium. Moreover, electrolytic dissociation ofend carboxyl groups in the polyamide resin is promoted by the effect ofthe basic material. The disassociated carboxyl groups (carboxylate ions)serve the purpose of a stabilized emulsifier in the aqueous dispersionmedium, enhancing the hydrophilicity of the polyamide resin as a wholeand preventing excessive aggregation between molecules in themanufacturing process. As a result, either of the aforementionedmanufacturing methods results in dispersion in an aqueous dispersionmedium of fine polyamide particles with a weight average particlediameter of 0.1-10 μm.

The aqueous dispersion of polyamide resin obtained in this way can beadjusted to the desired concentration using a suitable concentrationmeans such as a semipermeable membrane.

It is also possible to use the resulting aqueous dispersion of polyamideresin in the form of a fine powder obtained by a drying method such asspray drying, either as is or following solid-liquid separation bycentrifugation or filtration.

Next, the present invention is explained in more detail using examplesand comparative examples. However, the scope of the technical concept ofthe present invention is not limited by these examples.

EXAMPLE 1

In this example, the raw materials were placed in an autoclave equippedwith a turbine type agitator and a heating jacket, the autoclave wassealed, and an aqueous dispersion of polyamide resin was manufactured byheating the raw materials while applying shear force.

The autoclave had an internal diameter of 700 mm, a height of 1500 mmand a content volume of 450 L. The mixing blade had a diameter of 350mm. The heating jacket worked by the circulation of heated oil.

The raw materials were 120 kg of 6/66/12 copolymer nylon, 179.6 kg ofwater and 0.4 kg (10 mol) of sodium hydroxide. In the 6/66/12 copolymernylon, the ratio of end carboxyl groups to end amino groups was 87/13,and the amount of end carboxyl groups was 130 mmol per kg of polyamideresin.

The autoclave was heated to 150° C. and then maintained at 150° C. for30 minutes. The rotational speed of the mixing blade was 150 times aminute.

After being heated and mixed in this way, the contents of the autoclavewere cooled to 50° C., and removed from the autoclave as the aqueousdispersion of polyamide resin of the present invention.

In this aqueous dispersion of polyamide resin, the weight averageparticle diameter of the polyamide resin was 1.2 μm as measured with alaser diffraction particle size distribution meter (Shimadzu SeisakushoSALD 2000). Observation of the aqueous dispersion of polyamide resinafter it had been left for 1 month at 50° C. showed excellent standingstability, with absolutely no aggregative or floating disassociation ofthe polyamide resin.

EXAMPLE 2

In this example, an aqueous dispersion of polyamide resin wasmanufactured under the same conditions as in Example 1, except that theraw materials were 6/66/12 copolymer nylon having a ratio of endcarboxyl groups to end amino groups of 92/8 and an amount of endcarboxyl groups of 165 mmol per kg of polyamide resin, together with178.8 kg of water and 1.2 kg (21.8 mol) of potassium hydroxide.

In this aqueous dispersion of polyamide resin, the weight averageparticle diameter of the polyamide resin was 0.3 μm as measured with alaser diffraction particle size distribution meter (Shimadzu SeisakushoSALD 2000). Observation of the aqueous dispersion of polyamide resinafter it had been left for 1 month at 50° C. showed excellent standingstability, with absolutely no aggregative or floating disassociation ofthe polyamide resin.

EXAMPLE 3

In this example, the raw materials were 120 kg of 6/66/11/12 copolymernylon, 179.2 kg of water and 0.8 kg (20.0 mol) of sodium hydroxide. The6/66/11/12 copolymer nylon had a ratio of end carboxyl groups to endamino groups of 72/28 and an amount of end carboxyl groups of 170 mmolper kg of polyamide resin. Using these raw materials and an autoclavesimilar to that used in Example 1, an aqueous dispersion of polyamideresin was manufactured. The inside of the autoclave was heated to 170°C. and then maintained at that temperature for 30 minutes. Therotational speed of the mixing blade was 150 times a minute.

In the resulting aqueous dispersion of polyamide resin, the weightaverage particle diameter of the polyamide resin was 1.1 μm as measuredwith a laser diffraction particle size distribution meter (ShimadzuSeisakusho SALD 2000). Observation of the aqueous dispersion ofpolyamide resin after it had been left for 1 month at 50° C. showedexcellent standing stability, with absolutely no aggregative or floatingdisassociation of the polyamide resin.

EXAMPLE 4

In this example, the raw materials were 120 kg of 6/12 copolymer nylon,179.4 kg of water and 0.6 kg (10.7 mol) of potassium hydroxide. The 6/12copolymer nylon had a ratio of end carboxyl groups to end amino groupsof 88/12 and an amount of end carboxyl groups of 120 mmol per kg ofpolyamide resin. Using these raw materials and an autoclave similar tothat used in Example 1, an aqueous dispersion of polyamide resin wasmanufactured. The inside of the autoclave was heated to 170° C. and thenmaintained at that temperature for 30 minutes. The rotational speed ofthe mixing blade was 150 times a minute.

In the resulting aqueous dispersion of polyamide resin, the weightaverage particle diameter of the polyamide resin was 1.8 μm as measuredwith a laser diffraction particle size distribution meter (ShimadzuSeisakusho SALD 2000). Observation of the aqueous dispersion ofpolyamide resin after it had been left for 1 month at 50° C. showedexcellent standing stability, with absolutely no aggregative or floatingdisassociation of the polyamide resin.

EXAMPLE 5

In this example, the raw materials were 120 kg of 6/66/610/11/12copolymer nylon, 179.5 kg of water and 0.5 kg (12.5 mol) of sodiumhydroxide. The 6/66/610/11/12 copolymer nylon had a ratio of endcarboxyl groups to end amino groups of 66/34 and an amount of endcarboxyl groups of 120 mmol per kg of polyamide resin. Using these rawmaterials and an autoclave similar to that used in Example 1, an aqueousdispersion of polyamide resin was manufactured.

The inside of the autoclave was heated to 150° C. and then maintained atthat temperature for 30 minutes. The rotational speed of the mixingblade was 150 times a minute.

In the resulting aqueous dispersion of polyamide resin, the weightaverage particle diameter of the polyamide resin was 2.3 μm as measuredwith a laser diffraction particle size distribution meter (ShimadzuSeisakusho SALD 2000). Observation of the aqueous dispersion ofpolyamide resin after it had been left for 1 month at 50° C. showedexcellent standing stability, with absolutely no aggregative or floatingdisassociation of the polyamide resin.

EXAMPLE 6

In this example, the raw materials were 120 kg of 12-nylon, 179.2 kg ofwater and 0.4 kg (10.0 mol) of sodium hydroxide. The 12-nylon had aratio of end carboxyl groups to end amino groups of 85/15 and an amountof end carboxyl groups of 90 mmol per kg of polyamide resin. Using theseraw materials and an autoclave similar to that used in Example 1, anaqueous dispersion of polyamide resin was manufactured. The inside ofthe autoclave was heated to 200° C. and then maintained at thattemperature for 30 minutes. The rotational speed of the mixing blade was150 times a minute.

In the resulting aqueous dispersion of polyamide resin, the weightaverage particle diameter of the polyamide resin was 3.8 μm as measuredwith a laser diffraction particle size distribution meter (ShimadzuSeisakusho SALD 2000). Observation of the aqueous dispersion ofpolyamide resin after it had been left for 1 month at 50° C. showedexcellent standing stability, with absolutely no aggregative or floatingdisassociation of the polyamide resin.

Comparative Example 1

In this comparative example, the raw materials were 120 kg of 6/66/12copolymer nylon and 180.0 kg of water. In other words, no basic compoundwas included in the raw materials of this comparative example. The6/66/12 copolymer nylon was similar to that used in Example 1.

Using these raw materials and an autoclave similar to that used inExample 1, an aqueous dispersion of polyamide resin was manufactured.The inside of the autoclave was heated to 150° C. and then maintained atthat temperature for 30 minutes. The rotational speed of the mixingblade was 150 times a minute.

The contents obtained in this way were a lump of polyamide resin ratherthan an aqueous dispersion.

Comparative Example 2

In this comparative example, the raw materials were 120 kg of 6/66/12copolymer nylon, 179.6 kg of water and 0.1 kg (2.5 mol) of sodiumhydroxide. The 6/66/12 copolymer nylon was similar to that used inExample 1.

Using these raw materials and an autoclave similar to that used inExample 1, an aqueous dispersion of polyamide resin was manufactured.The inside of the autoclave was heated to 150° C. and then maintained atthat temperature for 30 minutes. The rotational speed of the mixingblade was 150 times a minute.

The contents obtained in this way were in the form of aggregatedpolyamide resin, not an aqueous dispersion.

Comparative Example 3

In this comparative example, the raw materials were 120 kg of 6/66/12copolymer nylon, 179.6 kg of water and 0.14 kg (3.5 mol) of sodiumhydroxide. The 6/66/12 copolymer nylon had a ratio of end carboxylgroups to end amino groups of 18/82, and an amount of end carboxylgroups of 30 mmol per kg of polyamide resin.

Using these raw materials and an autoclave similar to that used inExample 1, an aqueous dispersion of polyamide resin was manufactured.The inside of the autoclave was heated to 150° C. and then maintained atthat temperature for 30 minutes. The rotational speed of the mixingblade was 150 times a minute.

The contents obtained in this way were in the form of aggregatedpolyamide resin, not an aqueous dispersion.

Comparative Example 4

In this comparative example, the raw materials were 120 kg of 6/66/12copolymer nylon, 179.6 kg of water and 0.4 kg (10.0 mol) of sodiumhydroxide. The 6/66/12 copolymer nylon was similar to that used inComparative Example 3.

Using these raw materials and an autoclave similar to that used inExample 1, an aqueous dispersion of polyamide resin was manufactured.The inside of the autoclave was heated to 150° C. and then maintained atthat temperature for 30 minutes. The rotational speed of the mixingblade was 150 times a minute.

The contents obtained in this way were in the form of aggregatedpolyamide resin, not an aqueous dispersion.

What is claimed is:
 1. An aqueous dispersion of polyamide resin,comprising: dispersed polyamide resin particles, basic material andwater; wherein the weight average diameter of said dispersed polyamideresin particles is 0.1-10 μm; the ratio of end carboxyl groups to endamino groups in said polyamide resin ranges from 66/34 to 92/8; theamount of said end carboxyl groups is 90-170 mmol per kg of saidpolyamide resin; the amount of said basic material added is 0.2-3.0 molper mol of said end carboxyl groups; and said polyamide resin has as astructural unit at least one selected from the group consisting of—[NH(CH₂)₅CO]—, —[NH(CH₂)₆NHCO(CH₂)₄CO]—, —[NH(CH₂)₆NHCO(CH₂)₈CO]—,—[NH(CH₂)₁₀CO]— and —[NH(CH₂)₁₁CO]—.
 2. The aqueous dispersion ofpolyamide resin according to claim 1, wherein said basic material is analkali metal hydroxide or amino compound.
 3. The aqueous dispersion ofpolyamide resin according to claim 2, wherein said alkali metalhydroxide is sodium hydroxide or potassium hydroxide.
 4. The aqueousdispersion of polyamide resin according to claim 1, wherein theproportion of said water is 30-1500 parts by weight based on 100 partsby weight of polyamide resin.
 5. A method of manufacturing an aqueousdispersion of polyamide resin, comprising the steps of: adding polyamideresin to an aqueous dispersion medium containing 0.2-3.0 mol of basicmaterial per mol of end carboxyl groups in said polyamide resin, andcausing said polyamide resin to disperse in said dispersion medium aspolyamide resin particles; wherein the weight average diameter of saiddispersed polyamide resin particles is 0.1-10 μm; the ratio of endcarboxyl groups to end amino groups in said polyamide resin ranges from66/34 to 92/8; the amount of said end carboxyl groups is 90-170 mmol perkg of said polyamide resin; and said polyamide resin has as a structuralunit at least one selected from the group consisting of —[NH(CH₂)₅CO]—,—[NH(CH₂)₆NHCO(CH₂)₄CO]—, —[NH(CH₂)₆NHCO(CH₂)₈CO]—, —[NH(CH₂)₁₀CO]— and—[NH(CH₂)₁₁CO]—.
 6. The method of manufacturing an aqueous dispersion ofpolyamide resin according to claim 5, wherein said basic material is analkali metal hydroxide or amino compound.
 7. The method of manufacturingan aqueous dispersion of polyamide resin according to claim 6, whereinsaid alkali metal hydroxide is sodium hydroxide or potassium hydroxide.8. The method of manufacturing an aqueous dispersion of polyamide resinaccording to claim 5, wherein said aqueous dispersion medium contains30-1500 parts by weight of water based on 100 parts by weight of saidpolyamide resin.
 9. The method of manufacturing an aqueous dispersion ofpolyamide resin according to claim 5, wherein said polyamide resin isdispersed in said aqueous dispersion medium in a state where thepolyamide resin is heated to a temperature at or above the softeningtemperature of the resin.
 10. The method of manufacturing an aqueousdispersion of polyamide resin according to claim 9, wherein saidpolyamide resin is heated at a temperature of 70° C.-300° C.
 11. Themethod of manufacturing an aqueous dispersion of polyamide resinaccording to claim 10, wherein said polyamide resin is dispersed in saidaqueous dispersion medium with shear force applied to the aqueousdispersion medium to which the polyamide resin has been added.
 12. Themethod of manufacturing an aqueous dispersion of polyamide resinaccording to claim 11, wherein shear force is applied to said aqueousdispersion medium by rotation of a mixing blade.
 13. The method ofmanufacturing an aqueous dispersion of polyamide resin according toclaim 12, wherein the rotational speed of said mixing blade is 100-500rpm.